Articles, such as composite (or polymeric material) airframe structures of the type wing skins, fin skins, control surfaces, wind turbine blades, open rotor blades etc., having aerodynamic function, are designed and manufactured with a certain surface texture/roughness for enhancing the laminar airflow over the airframe's skin surface (i.e. the outer surface or aerodynamic surface of the article). The outer surface serves as an aerodynamic surface when the article is subjected for an air stream.
It is thus important that the aerodynamic surface is formed in such way that it becomes smooth. A smooth aerodynamic surface of the article gives a low fuel consumption of the aircraft, which is environmental-friendly.
The materials- and manufacturing technology used today, producing such outer surfaces, limits the aerodynamic efficiency of the airframe structures, e.g. regarding the possibility to achieve laminar air flow over a wing, fin, blade, control surface etc.
This can be solved by a proper coating of the airframe providing of a smooth skin surface, wherein the skin friction between the skin surface and the airflow is made as small as possible for achieving an optimal laminar airflow.
This can also be solved by using different techniques including the applications of different types of coatings onto the outer surfaces of the articles or infusions of different compositions into the article forming tool, for making a smooth outer surface of the article.
The articles are often formed and cured in forming tools made of resin matrix materials The blank to be conformed to the article often comprises fibre reinforced resin plies and is formed and cured on the forming surface of the forming tool.
One way to provide the article with a smooth surface is to provide a high surface smoothness of the forming surface of the forming tool for providing a good release of the finished article from the forming surface when the article is removed from the forming tool. A high surface smoothness of the forming surface thus provides for forming an article with high smoothness of the outer surface of the article.
U.S. Pat. No. 5,334,630 describes a mould surface made of phenol-aldehyde resole comprising silica fibres being treated with top coats for providing surface finish of the moulded product.
DE 19725984 describes one way to improve the surface smoothness of the article to be formed. Nano structure reinforced resins in the form of gelcoats are used between the forming surface of the forming tool and the surface of the article to be formed.
An object of the present invention is to provide a forming tool which is cost effective to produce, which forming tool simplifies the article forming procedure in production and promotes for a forming and curing cycle as short as possible for the article to be produced, wherein the finished aircraft article comprises a smooth outer surface (i.e. an optimal natural laminar airflow over the aerodynamic surface is achieved during flight).
It is thus desirable to provide an aircraft article forming tool comprising a forming surface, which forming tool provides a smooth outer surface of the finished article.
It is also desirable to make the forming surface scratch-resistant for preventing scratches in the forming surface, eventually caused by personnel during production, so that the finished aircraft article will have a smooth surface.
It is also desirable to decrease the problem with thermal expansion of the forming tool's forming surface, thereby promoting for a smooth surface of the finished article.
A further object is to provide an aircraft article forming tool which can produce large-scale and/or relatively thick articles having a smooth surface.
It is also an object to provide an aircraft article forming tool, which can produce articles having a complex curvature, which article at the same time will have a smooth outer surface.
A further object is also to eliminate the eventual drawbacks of known techniques.